Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-de06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 9E41C38000041; Wed, 10 Aug 2011 12:15:14 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1QrBPp-00036J-2b for rs_out_1@blacksheep.org; Wed, 10 Aug 2011 17:13:57 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1QrBPn-00036A-NQ for rsgb_lf_group@blacksheep.org; Wed, 10 Aug 2011 17:13:55 +0100 Received: from out1.ip01ir2.opaltelecom.net ([62.24.128.237]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1QrBPm-0000DI-Ge for rsgb_lf_group@blacksheep.org; Wed, 10 Aug 2011 17:13:55 +0100 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Au0AANOsQk5cHYAl/2dsb2JhbABCk20DhACPRXiBOwUBAQUIAQEDDS8NAg0PEAEBAwUCAQMRBAEBChcOFAEEGgYWCAYTCgECAgEBCodVviuGRgSCUJoqhn0 X-IronPort-AV: E=Sophos;i="4.67,351,1309734000"; d="scan'208,217";a="361943407" Received: from host-92-29-128-37.as13285.net (HELO xphd97xgq27nyf) ([92.29.128.37]) by out1.ip01ir2.opaltelecom.net with SMTP; 10 Aug 2011 17:08:46 +0100 Message-ID: <003e01cc5777$c33532b0$0401a8c0@xphd97xgq27nyf> From: "mal hamilton" To: References: <4E418609.6020500@iup.uni-heidelberg.de><67A6F7BF45BF4A0193A3DCB53000A283@PcMinto><008401cc56ce$2f1fb2c0$0401a8c0@xphd97xgq27nyf><12C475F3F4C84B818461753F2E8A60A6@PcMinto><4E41AECB.90808@iup.uni-heidelberg.de><8D68749D37B94275855FDBA46A3F6C97@PcMinto><4E427DFB.50801@iup.uni-heidelberg.de> Date: Wed, 10 Aug 2011 17:08:37 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2600.0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000 X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: Re: HB9ASB... Content-Type: multipart/alternative; boundary="----=_NextPart_000_003B_01CC5780.24C06240" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G X-AOL-SCOLL-SCORE: 0:2:442616640:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d40ce4e42ae924a09 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none This is a multi-part message in MIME format. ------=_NextPart_000_003B_01CC5780.24C06240 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable ----- Original Message -----=20 From: Andy Talbot=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Wednesday, August 10, 2011 4:30 PM Subject: Re: LF: Re: HB9ASB... I'm surprised so many seem to misunderstand how high impedance E-field = probes work. There is too much hearsay and false comments being = peddled. Stop thinking of the feeder as 'part' of the antenna as if it = were all one entity and consider each stage.... And forget that thing = called Ground completely. It starts with a high input-impedance amplifier which must have two = connections - ignore any common reference for now, it just has two input = pins. A voltage is imposed across these from any antenna with two = ports, like a short dipole. This input voltage is buffered, = amplified, and sent to the two output pins from which it travels down a = feeder - balanced, coax, or whatever - and into your receiver. So far = we haven't made any connection between input and output, and they could = (and ideally would) be independent and isolated from eachother However, they're not. One input connection is usually common with = one output - usually the 0V DC supply pin and the reference (and = please note, I am not referring to this as ground; ground is taboo, a = dirty word, and will not be mentioned) Which means the other = hot-side input pin now has a voltage imposed on it with respect to the = reference. This will probably come from a probe antenna which is = coupling to the E-field of a radiated signal. Now, bear in mind any = antenna must have two output ports, so where is the other side? As the = reference input pin is connected to the output reference pin, any other = connection to this point will form the other 'half' of the high = impedance short dipole antenna. Now, the feeder dropping down from the amplifier / probe assembly (or = across, or up and over, or buried in the soil [see, still didn't say the = taboo word] ) is connected to the input reference pin by virtue of the = amplifiers internally linking them, and must therefore form the other = half of the dipole. This is bad. We have a hi-Z dipole, with one = short element in the air where it should be, and the other element being = one conductor of a probably long length of feeder with its end connected = to we know-not-what. So what do we now have? A long assymetric dipole plus amplifier = assembly, stretching from some arbitrary shack connection up into free = space. The voltage at the not-middle of this is the stuff that is = amplified and fed to the receiver. So, as the bulk of the dipole is = close to the shack expect the majority of signal received to be locally = generated noise. =20 That is the case for a completely unscreened and un-earthed (still = didn't use the word :-) system. Picking up any locally generated = E-fields at high levels onto the dipole. =20 Now place the receiver and the rest of the local world with all its = noise and QRM generators in a screened room and make the feed coaxial = through a bulkhead connector into teh screened room and see what = happens. All the QRM is contained within the screened room and cannot = pass outside. The antenna is now a strange sort-of dipole with one = end in free space, and the other connected to a solid mass made from the = outside of the screened room. It can't pick up any QRM from inside the = screened room, and all it will now receive are signals generating an = E-field between the probe and the solid mass. Perfect! The shack and the rest of the world is not in a screened room, so = there lies the problem. However much you don't want it to be, with = this setup the feeder will always form the majority of the antenna = because there is nothing else there that can be the other half of the = dipole. And if the bottom end of the dipole intrudes into the rest of = the world, it will pick up stuff it shouldn't Andy So the FEEDER does form the majority part of this type of antenna, = simply one side of a very poor asymetrical dipole. It would appear this is not the antenna for a noisy urban environment The long element of the dipole is picking up every possible noise and = amplifying it and feeding all this noise plus signal to the RX, the = minute Probe element is insignificant.=20 This has been my observation all along. G3KEV Now, lets control the antenna structure all on its own and pretend the = feeder is not there at all. A true dipole would be nice although = impractical for now, so lets go back to the classic monopole which is = one half of a dipole, and the other half formed by the reflection of = this in a mirror, which is usually the surface of this planet called = Earth. Mount the amplifier assembly on a conductive pole with the = bottom end firmly connected to the surface of the mirror. Now, we have = a dipole formed of the complete assembly (mast plus probe) with its = reflection. It is not fed in the middle , but assymetrically near the = top where the short probe forms the other side from teh feed point. = The total length of the dipole is now twice the total height of = supporting mast and probe. As we're using a high impedance input = amplifier, if it nad a truely infinite input Z and zero capacitance, = the actual feed point wouldn't matter, it would always get the same = voltage imposed wherever the non-symmetrical spilt occurred. As Z and C = is finite it does make a difference so longer probes help with practical = amplifiers - but this is digressing. The antenna so far is ideal, and is no more prone to picking up local = QRM than any other antenna would be. But now we have to connect this = thing called a feeder, which introduces another arm to the dipole (a = tripole now perhaps ) which will ultimately go close to bad places. If = we could isolate the feeder by inserting a high common mode impedance = this would do the job, but it would have to be a near infinite = common-mode impedance, so is definitely not on. A transformer = coupling would help, but even that has high (relatively speaking) = capacitance across its windings, so will still leak common mode rubbish, = gettign worse at higher frequencies. And there is still the DC power = issue One solution is to bring the feeder down INSIDE the pole which must be = firmly connected to the reflecting surface of the mirror, maintain it = buried under the mirror's surface for as long as possible before it sees = the Badlands and hope that burying it will decouple any local QRM. Or = make the feeder non conductive like optical fibre. But there is still = the DC power issue. Which shows where the problems lie, and where to start thinking about = how to stop them. Separate dedicated mast firmly connected to the = mirror's surface. Feeder fed down inside it and buried. If coaxial = feeder is used - connect the braid at both ends to the mirror's surface = and bring in to the receiver input port coaxially and screened. DC = likewise - send it up the feeder. One solution, but its a difficult bit of hardware to build well, would = be a true differential input high impedance amplifier with a proper = equal length short dipole. The differential input - if ideal - will = inherently provide isolation between input and output ports but it does = have to be a perfect differential input, balanced antenna and so on. = Someone did mention to me once about using two identical active antennas = mounted end to end to form a a dipole, with the outputs from each = combined in a 180 degree hybrid combiner. That could prove viable, but = don't know if he ever tried it. Phew....! Andy www.g4jnt.com =20 2011/8/10 Stefan Sch=E4fer Hi Minto, Am 10.08.2011 13:10, schrieb Minto Witteveen:=20 Hi Stefan, (et al) Well I beg to differ.. :-) What I think happens is this: The outside of the coax picks up = electromagnetic radiation like any antenna (including QRM generated by = fluorescent lamps and Alinco switching power supplies). This signal = travels along the coax to the Miniwhip. (also in the direction of the = receiver but that is not important here as the signal is on the outside = of the coax). Upon arrival at the miniwhip this signal on the outside of the = coax has nowhere to go =ADbut to the _inside_ of the outer mantle of the = coax =96 it =91rounds the corner=92 at the end of the coax so to speak. I think the mechanism is that the unwanted signal on the screen = causes a potential difference between gate and source of the first = (J)FET. So this causes a current flow in the output stage and so a = signal at the RX input. A common mode choke between RX and the antenna ground should form a = low pass filter for unwanted signals coming from the shack. Using a = common mode choke without a local ground should have little effect, = except the coax is some 100m long (between choke and probe) ;-) Ah BTW regarding the discussion "the cable to the E field probe is = the actual antenna": One could just try what happens if one disconnects = the power supply. If the signal is still present then the cable is the = antenna, if the signal is gone: The probe must be the antenna. Isn't = it?! :-)=20 So how to avoid the QRM that is picked up by the coax to =91travel = back=92 via the inside: for the miniwhip it is indeed best (as Roelof = mentioned) to short these signals to earth _outside_ the house, = preferably as close to the miniwhip as possible. Grounding there would = to the trick, aided by a (large enough) common mode choke between the = ground point and the house. The QRM that is picked up in the house = would be =96 after attenuation by the choke - directed into the ground = and not up into the pole and the miniwhip. Yes yes, totally agreed.=20 Whatever happens in the house would then be largely irrelevant. = Adding a common mode choke close to the rig will do little extra. (it = would only attenuate QRM getting from the shack=92s earth system to the = outside of the coax). It would almost have the same effect (when ignoring the C between = cable and ground along to the choke near the antenna ground) as placing = the choke near the antenna ground, both are in series and increase the = current reducing impedance, yes...=20 Any signals picked up by the vertical coax between the earthing = point and the whip will add to the received signal, but at low = frequencies it will not be much. So far for theory. Now the proof of the pudding: DCF39 is now > = S9+40 dB. My old trusty QRM generator (Alinco SMPS) generates S9+25 at = 135.500. When I switch off the miniwhip (cut the power) DCF39 drops down = to just above the noise floor. As expected. Ah yes, that's what i meant above (should have read your mail = completely before answering ;-) ). This is the proof that Mal cannot be = right when saying "the coax is the actual antenna".=20 But the Alinco signal only drops down some 15 dB and remains the = only signal that is audible. This is exactly what I would expect: the = QRM travels along the outside of the coax to the miniwhip, =91rounds the = corner=92 and comes back via the inside of the coax shield. Further = proof that it indeed takes this route: if I disconnect the coax in the = shack the Alinco smps signal disappears also (so it is not received via = any other path). Hm, i rather expect a galvanic coupling i.e. stray currenty on the = supply cable of the RX. What happens if you run the RX on batteries? The = same dependency? There could be several reasons apply here...=20 Last year I already bought 3 meters of copper pipe to drive into = the ground in the backyard. Bet never got around to finish the job=85 Today it's nice WX here! And in NL?=20 The main reason the signal strength is much higher with the = elevated miniwhip is (I think) caused by the fact that I am surrounded = by other houses, gardens, trees etc. Not comparable with an open = field=85 Yes. 73, Stefan /DK7FC=20 Regards, Minto pa3bca = -------------------------------------------------------------------------= -=20 Ceterum censeo Carthaginem delendam esse -----Original Message----- From: Stefan Sch=E4fer Sent: Wednesday, August 10, 2011 00:03 To: rsgb_lf_group@blacksheep.org Subject: Re: LF: Re: HB9ASB... Hi Minto, Am 09.08.2011 22:48, schrieb Minto Witteveen: You are right w.r.t. the cable being (a significant) part of the = working of the Miniwhip antenna. [...] I don't think so. There should be no difference between a 5m and = 10m long cable. I think about a capacitive divider. The probe has = about 3 pF, that's one plate of the C. The other one is the cable and = metal connected. Once if this part of the C has say >10 * 3 pF, the = difference between longer cables become smaller and smaller. I think it is just the S/N that rises due to lower becoming noise = and higher signal levels. On a flat field without trees and houses, = you have excellent reception even with a 2m pole :-) 73, Stefan ------=_NextPart_000_003B_01CC5780.24C06240 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
 
----- Original Message -----
From:=20 Andy=20 Talbot
Sent: Wednesday, August 10, = 2011 4:30=20 PM
Subject: Re: LF: Re: = HB9ASB...

I'm surprised so many seem to misunderstand how high impedance = E-field=20 probes work.  There is too much hearsay and false = comments=20 being peddled.   Stop thinking of the feeder as 'part' of = the=20 antenna as if it were all one entity and consider each stage.... = And=20 forget that thing called Ground completely.
 
It starts with a high input-impedance amplifier = which must=20 have two connections - ignore any common reference for now, = it just=20 has two input pins.  A voltage is imposed across these from any = antenna=20 with two ports,  like a short dipole.   This input = voltage is=20 buffered, amplified,  and sent to the two output pins from which = it=20 travels down a feeder - balanced, coax, or whatever -  and into = your=20 receiver.   So far we haven't made any connection between = input and=20 output, and they could (and ideally would) be independent and isolated = from=20 eachother
 
However, they're not.   One input connection is usually = common=20 with one output - usually the  0V DC supply pin and the reference =  (and please note, I am not referring to this as = ground; ground=20 is taboo, a dirty word,  and will not be=20 mentioned)    Which means the other hot-side = input=20 pin now has a voltage imposed on it with respect to the = reference.  This=20 will probably come from a probe antenna which is coupling to the = E-field of a=20 radiated signal.   Now, bear in mind any antenna must have = two=20 output ports, so where is the other side?   As the reference = input=20 pin is connected to the output reference pin, any other connection to = this=20 point will form the other 'half' of the high impedance short dipole=20 antenna.
 
Now, the feeder dropping down from the amplifier / probe=20 assembly (or across, or up and over, or buried in the soil [see, = still=20 didn't say the taboo word] ) is connected to the input reference = pin by=20 virtue of the amplifiers internally linking them, and must therefore = form the=20 other half of the dipole.   This is bad.   We have = a hi-Z=20 dipole, with one short element in the air where it should be, and the = other=20 element being one conductor of a probably long length of feeder with = its end=20 connected to we know-not-what.
 
So what do we now have?  A long assymetric dipole plus = amplifier=20 assembly, stretching from some arbitrary shack connection up into free = space.   The voltage at the not-middle of this is = the stuff=20 that is amplified and fed to the receiver.    So, as = the bulk=20 of the dipole is close to the shack expect the majority of signal = received to=20 be locally generated noise.  
 
That is the case for a completely unscreened and un-earthed = (still didn't=20 use the word :-)  system.  Picking up any locally generated = E-fields=20 at high levels onto the dipole. 
 
Now place the receiver and the rest of the local world with all = its noise=20 and QRM generators in a screened room and make the feed coaxial = through a=20 bulkhead connector into teh screened room and see what=20 happens.   All the QRM is contained within the screened room = and=20 cannot pass outside.    The antenna is now a strange = sort-of=20 dipole with one end in free space, and the other connected to a solid = mass=20 made from the outside of the screened room.   It can't pick = up any=20 QRM from inside the screened room, and all it will now receive are = signals=20 generating an E-field between the probe and the solid mass. =20 Perfect!
 
The shack and the rest of the world is not in a screened = room, so=20 there lies the problem.   However much you don't want = it to be,=20 with this setup the feeder will always form the majority = of the=20 antenna because there is nothing else there that can be the = other=20 half of the dipole.   And if the bottom end of the dipole = intrudes=20 into the rest of the world, it will pick up stuff it shouldn't
 
Andy
 
So the FEEDER does form the majority part of = this type=20 of antenna, simply one side of a very poor asymetrical = dipole.
It would appear this is not the antenna for a = noisy=20 urban environment
The long element of the dipole is picking up = every=20 possible noise and amplifying it and feeding all this noise plus = signal to the=20 RX, the minute Probe element is insignificant. 
This has been my observation all = along.
 
G3KEV
 
 
 
Now, lets control the antenna structure all on its own and = pretend=20 the feeder is not there at all.  A true dipole would be nice = although=20 impractical for now, so lets go back to the classic monopole = which is one=20 half of a dipole, and the other half formed by the reflection of this = in a=20 mirror, which is usually the surface of this planet called = Earth.  =20 Mount the amplifier assembly on a conductive pole with the bottom end = firmly=20 connected to the surface of the mirror.  Now, we have a dipole = formed of=20 the complete assembly (mast plus probe) with its reflection.  It = is not=20 fed in the middle , but assymetrically near the top where the short = probe=20 forms the other side from teh feed point.   The total length = of the=20 dipole is now twice the total height of supporting mast and = probe.  =20 As we're using a high impedance input amplifier, if it nad = a truely=20 infinite input Z and zero capacitance,  the actual feed = point=20 wouldn't matter, it would always get the same voltage imposed wherever = the=20 non-symmetrical spilt occurred.  As Z and C is finite it does = make a=20 difference so longer probes help with practical amplifiers - but = this is=20 digressing.
 
The antenna so far is ideal, and is no more prone to picking up = local QRM=20 than any other antenna would be. But now we have to connect this = thing=20 called a feeder, which introduces another arm to the dipole (a = tripole=20 now perhaps ) which will ultimately go close to bad = places.  =20 If we could isolate the feeder by inserting a high common mode = impedance this=20 would do the job, but it would have to be a near infinite common-mode=20 impedance, so is definitely not on.    A  = transformer=20 coupling would help, but even that has high (relatively speaking) = capacitance=20 across its windings, so will still leak common mode rubbish, gettign = worse at=20 higher frequencies.  And there is still the DC power issue
 
One solution is to bring the feeder down INSIDE the pole which = must be=20 firmly connected to the reflecting surface of the mirror, maintain it = buried=20 under the mirror's surface for as long as possible before it sees = the=20 Badlands and hope that burying it will decouple any local = QRM.   Or=20 make the feeder non conductive like optical fibre.  But there is = still=20 the DC power issue.
 
Which shows where the problems lie, and where to start = thinking=20 about how to stop them.    Separate dedicated mast = firmly=20 connected to the mirror's surface.  Feeder fed down inside = it and=20 buried.   If coaxial feeder is used -  connect the = braid=20 at both ends to the mirror's surface and bring in to = the receiver=20 input port coaxially and screened.   DC likewise - send = it up=20 the feeder.
 
One solution, but its a difficult bit of hardware to build well, = would be=20 a true differential input high impedance amplifier with a proper equal = length=20 short dipole.   The differential input - if ideal - = will=20 inherently provide isolation between input and output ports but it = does have=20 to be a perfect differential input, balanced antenna and so = on.  =20 Someone did mention to me once about using two identical active = antennas=20 mounted end to end to form a a dipole, with the outputs from each = combined in=20 a 180 degree hybrid combiner.  That could prove viable, but don't = know if he ever tried it.
 
Phew....!
 
Andy

 
 
 
 
 
2011/8/10 Stefan Sch=E4fer <Stefan.Schaefer@iup= .uni-heidelberg.de>
Hi=20 Minto,

Am 10.08.2011 13:10, schrieb Minto Witteveen:=20

Hi=20 Stefan, (et al)

Well I beg to differ.. :-)
What I think = happens=20 is this: The outside of the coax picks up electromagnetic = radiation like=20 any antenna (including QRM generated by fluorescent lamps and = Alinco=20 switching power supplies). This signal travels along the coax to = the=20 Miniwhip. (also in the direction of the receiver but that is not = important=20 here as the signal is on the outside of the coax).
Upon arrival = at the=20 miniwhip this signal on the outside of the coax has nowhere to go = ­but=20 to the _inside_ of the outer mantle of the coax =96 it =91rounds = the corner=92=20 at the end of the coax so to speak.
I think = the=20 mechanism is that the unwanted signal on the screen causes a = potential=20 difference between gate and source of the first (J)FET. So this = causes a=20 current flow in the output stage and so a signal at the RX = input.
A=20 common mode choke between RX and the antenna ground should form a = low pass=20 filter for unwanted signals coming from the shack. Using a common = mode choke=20 without a local ground should have little effect, except the coax is = some=20 100m long (between choke and probe) ;-)

Ah BTW regarding the=20 discussion "the cable to the E field probe is the actual antenna": = One could=20 just try what happens if one disconnects the power supply. If the = signal is=20 still present then the cable is the antenna, if the signal is gone: = The=20 probe must be the antenna. Isn't it?! :-)=20



So=20 how to avoid the QRM that is picked up by the coax to =91travel = back=92 via=20 the inside: for the miniwhip it is indeed best (as Roelof = mentioned) to=20 short these signals to earth _outside_ the house, preferably as = close to=20 the miniwhip as possible. Grounding there would to the trick, = aided by a=20 (large enough) common mode choke between the ground point and the = house.=20  The QRM that is picked up in the house would be =96 after = attenuation=20 by the choke - directed into the ground and not up into the pole = and the=20 miniwhip.

Yes yes, totally agreed.=20

Whatever=20 happens in the house would then be largely irrelevant. Adding a = common=20 mode choke close to the rig will do little extra. (it would only = attenuate=20 QRM getting from the shack=92s earth system to the outside of the=20 coax).
It would almost have the same effect = (when=20 ignoring the C between cable and ground along to the choke near the = antenna=20 ground) as placing the choke near the antenna ground, both are in = series and=20 increase the current reducing impedance, yes...=20


Any=20 signals picked up by the vertical coax between the earthing point = and the=20 whip will add to the received signal, but at low frequencies it = will not=20 be much.
So far for theory. Now the proof of the pudding: DCF39 = is now=20 > S9+40 dB. My old trusty QRM generator (Alinco SMPS) generates = S9+25=20 at 135.500. When I switch off the miniwhip (cut the power) DCF39 = drops=20 down to just above the noise floor. As = expected.
Ah=20 yes, that's what i meant above (should have read your mail = completely before=20 answering ;-) ). This is the proof that Mal cannot be right when = saying "the=20 coax is the actual antenna".=20

But=20 the Alinco signal only drops down some 15 dB and remains the only = signal=20 that is audible. This is exactly what I would expect: the QRM = travels=20 along the outside of the coax to the miniwhip, =91rounds the = corner=92 and=20 comes back via the inside of the coax shield. Further proof that = it indeed=20 takes this route: if I disconnect the coax in the shack the Alinco = smps=20 signal disappears also (so it is not received via any other=20 path).
Hm, i rather expect a galvanic coupling = i.e.=20 stray currenty on the supply cable of the RX. What happens if you = run the RX=20 on batteries? The same dependency?
There could be several reasons = apply=20 here...=20


Last=20 year I already bought 3 meters of copper pipe to drive into the = ground in=20 the backyard. Bet never got around to finish the=20 job=85
Today it's nice WX here! And in NL?=20


The=20 main reason the signal strength is much higher with the elevated = miniwhip=20 is (I think) caused by the fact that I am surrounded by other = houses,=20 gardens, trees etc. Not comparable with an open=20 field=85
Yes.

73, Stefan /DK7FC=20




Regards,
Minto=20 = pa3bca






--------------------------------= ------------------------------------------=20
Ceterum censeo Carthaginem delendam esse
-----Original = Message-----=20 From: Stefan Sch=E4fer
Sent: Wednesday, August 10, 2011 = 00:03
To: rsgb_lf_group@blacksheep.org
Subject: Re: = LF: Re:=20 HB9ASB...

Hi Minto,

Am 09.08.2011 22:48, schrieb = Minto=20 Witteveen:
You=20 are right w.r.t. the cable being (a significant) part of the = working of=20 the Miniwhip antenna. [...]

I don't think = so. There=20 should be no difference between a 5m and 10m
long cable. I = think about=20 a capacitive divider. The probe has about 3
pF, that's one = plate of the=20 C. The other one is the cable and metal
connected. Once if this = part of=20 the C has say >10 * 3 pF, the difference
between longer = cables=20 become smaller and smaller.

I think it is just the S/N that = rises=20 due to lower becoming noise and
higher signal levels. On a flat = field=20 without trees and houses, you have
excellent reception even = with a 2m=20 pole :-)

73,=20 = Stefan


------=_NextPart_000_003B_01CC5780.24C06240--